In material machining processes, the quality of the process result is crucially dependent on the stability of the process parameters, which is why process parameters that can change in an uncontrolled manner during the machining process are monitored and also readjusted.
A known measure in laser material machining is to monitor the fluctuations of the laser power by coupling out a certain portion of the laser beam and routing it to a radiation-sensitive sensor. The received signal can then be used to regulate the laser power.
Monitoring the laser machining process by detecting radiation coming from the area of interaction between the laser beam and the workpiece is also known. For this purpose a dichroic mirror, for example, which allows the laser radiation to pass without hindrance but reflects the radiation coming from the interaction area onto a sensor, is inserted into a laser machining head via which a laser beam is focused onto a workpiece. The characteristics of the radiation detected by the sensor can differ in intensity, intensity distribution and wavelength, depending on the conditions in the interaction area. Changes in the radiation characteristics, and thus the received signals that are obtained, are caused by fluctuations of several process parameters. In particular, these can be fluctuations of laser power, feed rate, focus position, the locally differing heating of the workpiece, the supplying of protective gas, and the gap width in laser welding. That is to say, the receiver signals do not represent the fluctuations of individual process parameters such as the focus position, but instead only allow inferences regarding the quality of the process result as a whole, e.g., the weld seam, the cut, or the drill hole. Process monitoring of this type primarily therefore mainly serves to monitor the success of the process.